Abstract: The low molecular weight polyisoprene (LPI) after anionic polymerization was modified by 3-chloropropyl alkoxysilane, and the conditions for this end-capped modification were investigated. The structure of LPI terminated with alkoxysilane was characterized using Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance spectroscopy (¹H-NMR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Additionally, the end-capped ratios of the modified products were calculated using ¹H-NMR hydrogen spectra. Results indicated that the reaction occurred at the end of the molecule, which had little effect on the microstructure, glass transition temperature and heat resistance of the product. However, it leads to a slight decrease in the number average molecular weight and an increase in the molecular weight distribution index. The end-capped ratio increased with the increase of termination reaction temperature, and decreased significantly with the increase of the amount of 3-chloropropyl alkoxysilane. When the termination reaction was conducted at 50 ℃ with an equivalent amount of terminator to initiator, the end-capped ratio reached 91.35%.